Project Summary. Dr. Williams'immediate career goal is to establish himself in the field of nuclear receptor signaling in cancer, with a longer term goal of establishing a career in cancer research focusing on the cross talk between signal transduction pathways as it pertains to cellular signaling in cancer. In conjunction with his previous experience in receptor tyrosine kinase signaling, the proposed research plan will arm Dr. Williams with a well rounded and comprehensive skill set to launch his career as an independent scientist. In addition to laboratory research, Dr. Williams will participate in research focus groups, with which he'll discuss pertinent scientific issues, and present data regularly. Furthermore, he will present his findings at national and local scientific meetings. Tulane Cancer Center facilities will be at Dr. Williams'disposal, and the expertise of tenured faculty to help guide his research. Dr. Williams will study the therapeutic, prognostic and mechanistic aspects of ER( phosphorylation at 4 newly identified sites. Preliminary results show a dramatic impact of these sites on transcriptional activity of ER(. This proposal hypothesizes that novel phosphorylation sites identified in ER( (at serines 47, 282, 294, and 559) will impact tamoxifen effects on growth of tamoxifen-sensitive and -resistant breast cancer cells through mechanisms that alter ER( transcriptional activity. Aim 1 will test the hypothesis that ER( phosphorylation at S47, S282, S294, and S559 regulates ER( transcriptional activity, growth of breast cancer cells in culture, and in vivo tumor formation, Aim 2 will identify the kinase signaling pathways that regulate ER( phosphorylation. Aim 3 will mechanistically address how ER( phosphorylation at serines S47, S282, S294, S559 regulates ER( activation in response to ligand including ER( dimerization, DNA binding and coregulator recruitment. Aim 4 will ascertain the clinical significance of ER( phosphorylation at serine 47, 282, 294, and 559 in primary breast tumors (IHC staining). Relevance. Characterization of novel ER( phosphorylation sites will lead to a better understanding of the mechanisms underlying therapeutic resistance in breast cancer. Furthermore these studies may lead to improved therapeutic regimens for breast cancer patients, by targeting kinases associated with resistance.